MW dissertation claims that screwcaps cause more wine damage than cork

wine science

MW dissertation claims that screwcaps cause more wine damage than cork


The rise in screwcap use in Australia since 2000 has been remarkable. Now they are by far the majority closure, for fine wines as well as more commercial ones. But a Masters of Wine (MW) dissertation by Alison Eisermann-Ctercteko, which has been published in Australian trade publication Wine and Viticulture Journal, presents evidence that is claimed to show that screwcaps cause more damage to wine than cork.

Eisermann-Ctercteko surveyed 22 retail outlets, most in the Sydney area, and examined some 11 500 bottles. The level of damage, if any, was graded on a five-point scale. Wines sealed with damaged screwcaps were then analysed for free and total sulfur dioxide (SO2) and browning (absorbance at 420 nm). Loss of free SO2 and browning are both signs of oxidation.

The results of these studies were alarming. The overall physical damage level of the screwcapped wines was 26%. 8.2% of screwcapped wines were damaged enough for significant changes to be detected in both browning and free SO2 levels.

In addition, 7.2% of screwcaps were applied incorrectly, or there was a fault in the application, but most of these defects were merely cosmetic.

She also found that printed screwcaps were more likely to show damage than plain ones. The Stelvin Lux, with its internal plastic seal, showed very little damage, but this closure is more expensive.

‘Screwcap damage is a significant issue and shown to be surprisingly high in retail at a level of 8.2% of screwcapped bottles,’ says Eisermann-Ctercteko. ‘This is greater than the previous industry-wide problem of cork taint which led to the rapid change in closure type. This requires immediate resolution, as these levels are unacceptable.’

Screwcap supporters will argue that cork taint is more of a problem than the levels of oxidation seen in these wines because cork taint renders a bottle undrinkable. However, producers will be alarmed that 8% of their bottles are showing signs of oxidation because of the closure.

NOTE ADDED LATER: I have seen the original dissertation, and I disagree with the interpretation of the data. You can read my comments  here

42 Comments on MW dissertation claims that screwcaps cause more wine damage than corkTagged ,
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42 thoughts on “MW dissertation claims that screwcaps cause more wine damage than cork

  1. Interesting and worrying at the sane time. So where does this leave us wine producers? At one end of the supply side we have bacteria infecting cork trees and that the other end, if we’ve gone down the screwcap route, we’ve got ingress of oxygen due to poor bottle handling (more than likely at the retail end of the chain as damage to scewcaps on fully automated bottling lines is rare).

    So we can put cars on Mars and men on the moon, but we still haven’t figured out how to close wine. Or are Diam and Nomacork the winners now?

    Which way do you suggest we go Jamie?


  2. It appears to be a condemnation of the handling channels from bottling line to store shelves…… not the screw caps seal…. well I guess it is the seal that has been broken, careful handling may take care of 90% of the problem……

  3. Jamie – if you’d like a copy of the dissertation, e-mail Penny Richards, the executive director of the IMW. As long as the dissertation is not confidential for commercial reasons, and the author is amenable, Penny will most likely gladly send it to you.

  4. No, she didn’t open 11 5000. She just examined them for signs of damage. And then analysed some with damage.

    I’m going to email Penny to see if I can get the dissertation.

    Mike, cork taint runs at about 3.5% in large studies. So 8.2% is more. As a producer you have few issues: the question is, do your customers? This applies to all closures.

  5. There are a lot of questions about this study that need to be answered before it is useful (to me at least).
    I’d like to know which retailers where examined, or at least which type of retailer. I’d expect a higher % of damage in the big liquor barns than I would in a smaller specialist retailer. What price points were the faulty bottles found at. I’d expect less care to be taken with a less valuable product in these places. In some of the really cheap wines, oxidation is going to be the least of the problems with the wine.
    As indicated, there are different quality levels in screwcaps so it would be interesting to see how the faults breakdown across the quality levels.
    If, on the rare occasion, I am buying from a retailer, I will always check the screwcap for any sign of damage anyway.

  6. man, if cork taint were the only problem, i’d almost be happy with them. but the oxidation of wines through POOR CORK MATERIAL is far, far, faaaaaaaar greater than the problem with TCA, i really struggle to understand how the focus on cork is on taint: STUFF taint, it’s a minor concern next to corks so faulty the goddamn wine leaks out of the bottle- i’ve seen this with screwcaps too, sure, but it’d be a fraction of the rate of leaky/porous corks.
    i’ve dinged screwcaps myself, they’re relatively easy to gently hammer flat or tighten further to preserve the seal …….but what can anyone do about crappy corks? there’s just no way of knowing til you get the foil off and see leakage; and even then, some that have not obviously leaked have awful corks too! i now remove all foils completely before long term storage to ensure they are (visibly) OK, and CERTAINLY strip them from all auction purchases which have an even greater variability. have only bought one screwcapped wine at auction that was rooted, against so many poor cork sealed ones that i don’t even wanna start thinking about it.

  7. Bravo hughthewineguy ! All the discussion about cork taint diverts from the fact that cork is a shit long term closure, it fails far more than it should. Jamie, if our customers had a problem with screwcaps they would tell us, the reverse is true, they love them and they tell us so. To quote an 8.2% failure rate without a broad sample really is a nonsense as is comparing it to a 3.5% failure rate from cork, where did that number come from anyway? Cork suppliers remind me of the tobacco companies in the 70’s and 80’s, just keep denying until the market dictates otherwise. Aren’t we lucky cork isn’t addictive.

  8. At least with screw caps, its a yes/ no proposition, they’ll leak straight away. Either the wine is oxidised or not. Cellaring or buying with cork is full of nasty time fuse surprises. “Dissertation” is a bit rich, it implies MW is an accredited educational institution. Lets see a peer review then and some control versus treatment.

  9. Personally I have no urge to indulge the cork haters nor cork lovers in a debate anymore.
    What doesnt get mentioned by anyone is the bottle manufacturers. The consistancy of the bottle neck (for corks) and lip (for screwcaps) is highly important to obtain a proper seal. Obviously this does not address TCA, but a side note TCA or TBA is not exclusive to cork- I have had my fair share of “corked” wines under screwcap.
    The amount of flimsy poorly cast bottles can very well explain a fair chunk of oxidation in both cork and screwcap results.

  10. How about IWC fault clinics? Did they found a similar percentage of such faults in screwcapped wines? (Though quite possibly they don’t track if screwcaps were visibly damaged or not.)

  11. I have not found this level of failure rate (8.2%) within my dealings with screwcap wines, and find overall the screwcap option to be a better offering than traditional cork (even though it goes against all training, history and the general love of a traditional closure)

    Would be interested to see your review Jamie and hear your experiences

  12. Jamie,

    Thank you for posting this.
    It does seem to have a whole series of flaws. As you mention it was not controlled, then second she tested only the bottles that she examined and picked from a sample size of 11500 bottles. This seems extremely selective and almost certain to produce the result you are looking for in the first place. ie a non controlled, non random and non blinded study.

    Additionally she looked at only sauvignon blanc from what I can determine from the title. It would be very interesting to know the average age of bottles that were selected.

    The 8.2% figure does seem so far above the the normal experience of consumers, such as myself, it would be interesting as pointed out, to see how this compares to the IWC figures, which from memory have never been so high.

  13. Jamie,

    Would be great to see the study itself. While screwcaps are most likely a safer closure it is true that the handling post bottling and the quality of the application (machine, glass quality etc…) is more important than with corks. I have seen bad glass give you a 15% failure rate. One cannot assume that because you use a screwcap you won’t have a problem.

  14. Never cared for screwcaps as the seal contact area is too small for aging. Even the stelvin which is best is too small and consists of saranex to make a good seal and it is no longer used in saran wrap as it leaches plasticizers in acidic mediums. I have wines corked in my cellar from wines I made over 30 years ago. Sure there is some seapage of wine through the cork, but the wines I’ve opened still have aged gracefully and are not overly oxidized. As such I have switched to DIAM corks (or predecessor) over 12 years ago after taint issues. I would believe as far as bottles are concerned with the much greater seal surface area of corks or DIAM version (as well as greater elasticity of these materials) are much more forgiving of any irregular bottle necks. Plastic corks on the other hand do not seem to yet have the right elasticity as well as oxygen permeation for aging, despite some claims and proprietary research.

  15. I had a stack of 8,000 cases of screwcaped wine fall over a few years back (pallet failure, 4 high stack).
    The 4 pallets of dented caps we found in the cleanup and reboxing/labeling project were consumed by friends of the winery and sold through a local store. Even bottles with big dent caps were fine a year later and this was a delicate wine.
    I left corks for the same reasons as Mike and Hughthewineguy above and agree totally with Mike, corks (cheap ones anyway) are shit!

  16. Quite a provocative title but it blames the cap rather than where the problem really lies – if the claims are valid, it illustrates a major problem with handling. Obviously if handled properly, there would be no air leaks. The susceptibility of cap liners to leak air after denting is a secondary issue. Yes, liners should be sufficiently robust to withstand small dents in the rim but there will be limts. Certainly if the seal to the bottle is marginal due to poor application or glass issues, dents in the rim are more likely to allow the passage of air. I find it very hard to believe that printed caps would be any different than plain caps. Additional questions come to mind – liner construction, time after bottling. Hmmm, makes me happy I am (semi) retired so I won’t get tasked with OTR testing of hundreds of dented caps.


  17. when is the world going to wake up to the fact that the MW is not an academic accreditation…this is not peer reviewed…an obvious reason why Universities don’t align themselves with MWs..where is the credibility in this paper if it hasn’t been peer reviewed…come on folks keep science scientifiv

  18. Regardless of the methodology in this study, it is sufficient evidence to do more research and hopefully publish in a peer reviewed journal. What a great thesis subject for some bright young thing out there! Cheers!

  19. This is just another study about closures and their ability to function without altering too much the wine integrity. Indeed, the screwcap does require much tighter tolerances between the glass finish, the tension and condition of metal disc rollers on the applicator and this varies from bottling line to bottling line and from glass supplier even to capsule pliability. There is also a winemaking component that must be addressed when using screwcaps to avoid spoilage. It is a technical closure difficult to tame that seems to works great for spirits but in the wine segment we still have a lot to understand. The cork is much more forgiving, no doubt and manufacturers have done tremendous efforts to eliminate the taint that existed 10 or 15 years ago. Most wineries started using screwcaps for economical reasons and not so much for TCA contamination. It makes money sense; one closure, one machine, less time, less maintenance, no need to buy a cork and a capsule. We sell all components but we have noticed a possible slow down in the use of screwcap for wine and more classic and environmental approach to great quality natural cork.

  20. I posted on the FB link, but a condensation here:
    Both, indeed all, closures have flaws and advantages. The bottom line is ease of use and maintaining quality. Screwcaps have both, but her dissertation shows a different result. Without seeing the paper and examining specific methods used, it may (or may not be) just another paper that started out with a thesis and worked to prove it.
    Mr. Amaro’s comments are spot on. I would urge readers to think past the “either/or” mindset, and examine the larger picture, particularly regarding the environment, as this is key, with very few people are addressing regarding screw caps. It requires more than a knee jerk response. Some critical thinking on both sides is in order.

  21. We use Stevin Lux which was given a clean bill of health. The issues lied with the wine preparation to ensure that wines are set up for this type of closure rather than the closure it self being the root cause Handeling of the cap and application is essential as it can be knocked which affects the thread and therefore the seal. Even a Sydney at the top of the cap can affect the seal. Lux is more robust because it has an internal thread . Good to note that there were no corked wines in he tria. to finish off all wines can be subject to oxidation and faults cause by poor handling and lack of appropriate QA.

  22. No response from the IMW yet so I still haven’t seen the original dissertation. It would be interesting to know whether the cost of this work was funded in any way, or whether Alison alone picked up the tab. It would also be interesting to know why this wasn’t published in a peer-reviewed journal rather than a trade magazine, because it is an important topic. I am not suggesting the results aren’t valid, just that they need to be subject to proper scrutiny

  23. I’m working as a wine-writer, critic and judge since more than 25 years, nearly all over the world, mostly in Europe. Since more than ten years I am glad to have much mor screwcaps than cork, because I don’t have to throw away so many bottles.
    I do my own figures about some thousand bottles. And this shows exactly the other way round. Wine under screwcaps nearly never shows any problem. Wine under cork are very often tainted. And the problem are not the pur TCA-stinkers. It’s the problem of different bottles. If you open a case of 12 and you find 4 bottles that are sensorical the same, you got perfect corks. So, I really don’t beleive in the result of this dissertation, not even, if she tried discounter wines, sorry. But if someone wants to do a large tasting-counting for a real university-level result, to show how it is really, I’m the first to help…

  24. Screwcap is like watching Mona Lisa on a full HD monitor and Cork is the real deal at Louvre . The first one will “live forever” the second one requires more attention and could go bad anytime . Which one would you prefer?

  25. What separated or identified the bottles that were subjected to excessive temperature storage at various points in the supply chain? Considering responsibility for damage to wine, this is a far more prevalent problem than closure choice. Could it be that screw-capped wines are subjected to more careless mis-handling because they are considered “safe”? There are simply too many factors and variables in the mix to take this type of narrowly-targeted study very seriously. By the way, I opened a screw-cap closed Quixote 2001 Napa Valley Cabernet Sauvignon last week that had been stored under perfect conditions for the past decade + since acquisition … it was unbelievably both fruity and tannic, as if newly-released. I was amazed (and, frankly, disappointed!).

  26. I had tastings with wines under screwcaps 30 years back. Compared to thie corked ones, the Mona Lisa is screwed 😉 and the Louvre is on the table of the coroner…

  27. Really, really bad analogy, Razvan (as if any monitor will work inndefinitely, etc. etc.)

    How about screwcap is like looking at the original Mona Lisa painting in the Louvre, preserved as sensible and efficiently as current technology allows? And cork is like looking at the original Mona Lisa painting that someone took a nice fat dump on? A completely natural, traditional and bio-degradable dump that made an impressive sound, of course.

  28. Screwcap is just about marketing and getting the product cheap on the table, they were not developed because it preserves wine better. The fact that is indeed neutral and if not dinged it will last better is just a plus. Make no mistake, if there was a cheaper way it will make the screwcap a complete bad boy, scientifically. I rather drink cheap wine from the box and have the long lived good wines under cap.

  29. Razvan,
    Good luck to you and the rest of the Creationists and Flat Earth Society members. Like those “debates”, it is ridiculous that this one is still going. Please do enjoy your goon-bag. It would seem that large amounts of cheap wine couldn’t make you any more irrational.

  30. I recently ordered six bottles from a Washington winery and received them yesterday. Of the six, two were leaking from the screwcaps and one had visible sedimentation. This was a 2011 vintage.

    Is the wine from the leaking bottles safe to drink? I do not see any discoloration but the level of wine is noticeable, probably around 1/8 cup in each bottle.

    Bottles were shipped cross-country.

  31. I lobby for quality bottles and quality natural corks (ie not composite corks).

    We have not discussed other issues here such as the carbon sink of cork versus the relatively high carbon footprint of aluminium caps. That the oak forests of Portugal (52% of cork originating in Portugal) are habitat for the endangered Iberian lynx and Iberian eagle, to mention a couple of species. These forests are being replaced with alien eucalypt forests if cork is no longer commercially viable.

    Natural corks are more easily recyclable and are being recycled (see project spearheaded by the Savoy Hotel in London).

    I haven’t seen discussion of the problem of sulphidisation in screw-capped wine said to be as high as 2%

    Australia still produces 50% of its wine with corks, but only for the export market. Consumers in Australia are being bullied to accept aluminium screw caps.

    For supporters of natural cork-sealed wines (not composite cork), please visit As a consumer lobby group we can ensure a choice in future of wine sealers.
    Cheers! Geoff

  32. The assertion that “Consumers in Australia are being bullied to accept aluminium screw caps” is absolute, biased garbage. Where companies have offered both cork and screwcap , invariably they have had trouble selling the cork version.
    Possiby, our greatest Chardonnay producer, Giaconda, ever so reluctanly offered a screwcap version years ago. The winemaker actively pressed his view that cork was the preferred closure.
    For this year’s release, he has announced that ONLY screwcap will be offered due to the overwhelming demand of his consumers.
    Other wineries, such as Cullen, who produce one of Australia’s greatest reds ONLY offer screwcaps.
    People such as Geoff Holland really should be pulled up for such misleading statements.The facts clearly are that the great majority of consumers in Australia demand screwcap or, in the case of Sparkling Wines, Crown seals.
    Again, with the crown seal, Seppelts had great difficulty selling the cork version of their Show Reserve Sparkling Shiraz, so now only offer the vastly superior crown seal.
    Australian consumers have DEMANDED screwcaps. Fact!

  33. I have been disappointed quite a lot recently by screw cap wines that don’t taste like I know they should. I recently returned a half dozen of Villa Maria Sauvignon Blanc 2016. I tried 5 of them and they ranged from not good to undrinkable. I left the 6th unopened for the retailer to make his own assessment.

    I won’t buy a white wine with a screw cap if it is more than a year old.

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